1. Field of the Invention
The present invention relates to a forging or heading method for hollow articles, which is suitable for providing plastic processed hollow articles having a circumferential groove formed in its outer surface.
2. Description of the Related Art
In producing a hollow article having a circumferential groove formed in the outer surface and a through hole formed at the center, like the one shaped as shown in, for example, in FIG. 6, a conventional manufacturing process involves a cutting process.
In forming a circumferential groove in the outer surface of a columnar material by cutting work, however, excessive processing time is needed, reducing the productivity. As well, cutting wastes or chips are produced, reducing the yield and deteriorating the working environment.